1. Field of the Invention
The present invention relates to an apparatus and method for monitoring the qualities of optical signals in optical transmission systems or photoelectric transmission networks employing a light amplifier, and more specifically to an apparatus and method for monitoring the qualities of the optical signals using the amplitudes of clocks.
2. Description of the Conventional Art
The U.S. Pat. No. 5,654,816 entitled xe2x80x9cQualities monitoring and fault location in optical transmissionxe2x80x9d disclosed a technique for monitoring the qualities of optical signals for optical transmission systems. The U.S. Pat. No. 5,513,029 entitled xe2x80x9cMethod and apparatus for monitoring performance of optical transmission systemxe2x80x9d disclosed a technique for monitoring the performance of optical transmission system.
As light amplifiers capable of direct amplification of light are commercialized recently for optical transmission systems, transmission distance of optical transmission systems remarkably increases. Now, optical transmission systems whose relayless transmission distance amounts to several hundreds of kilometers are commercially available. Also, a number of studies have been performed on the photoelectric transmission networks, which achieve line distributions and branch connections without converting optical signals into electrical signals. This photoelectric transmission network is expected to be used as a major infrastructure of transmission networks in the forthcoming information superhighway era.
However, in order to utilize transmission systems efficiently, it should be noted that these systems are managed and maintained based upon the qualities of the optical signals carrying the information such as the optical signal intensity, the signal to noise ratio, and the error rate upon receiving the signal. Also, the reliability of communication needs to be assured.
In conventional optical communications that do not employ light amplifiers, the quality information of the optical signal needed for the management and maintenance of the systems can be correctly detected by converting optical signals into electrical signals at relay that relays the optical signal or at the receiving terminal of optical signals.
However, since systems using light amplifiers employ light amplifying relays instead of conventional electrical relays, light amplifying relays don""t convert optical signals into electrical signals. Optical signals are not to be converted to electrical signals even in the nodes of the photoelectric transmission networks as well, and thus branch connections or line distributions are performed in the form of optical signals. Accordingly, the method capable of detecting the quality information of the optical signal needed for the management and maintenance of the systems or networks depends only upon the measurement of the signal to noise ratio of optical signals. Results of this measurement provide only smaller portion of the information than needed. For example, when optical signals do not carry any meaningful data, it is supposed to be determined as normal state by measuring only the intensity of optical signals, but communication fails in practice
The object of the present invention is providing an apparatus and method for monitoring the qualities of optical signals such as the presence or absence of the signals and the error rates upon receiving signals. It extracts clock components from the transmitted optical signals and measures magnitude of the clock amplitude in light transmission systems or photoelectric transmission networks.
To achieve this object, the monitoring apparatus according to the present invention is characterized by comprising:
an optical signal processing means for separating a portion of optical signals from the optical signals in transmitting through an optical fiber and converting the separated portion into signals having clock components;
a narrow optical detection means for converting the optical signal outputted from the optical signal processing means into electrical signals and then extracting only clock frequency components from the electrical signals to output the extracted components as sine waves;
a super high frequency (SHF) rectifying means for converting the output of the optical detection means into direct current (DC) signals;
a voltage detection means for measuring the magnitude of the direct current signals outputted from the SHF rectifying means; and
a means for monitoring the qualities of the optical signal using the magnitude of the voltage, corresponding to the clock amplitude, outputted from said voltage detection means.
Also, the monitoring method according to the present invention is characterized by comprising the steps of:
separating a portion of an optical signal from the optical signal in transmitting through an optical fiber and converting the separated portion in to a signal having clock components;
converting the optical signals outputted in the separating step into electrical signals and then extracting only clock frequency components from the electrical signals to output the extracted components as sine waves;
converting the output of the converting the optical signals step into direct current (DC) signals;
measuring the magnitude of the direct current signals outputted in the converting the output step; and
monitoring the presence or absence of data and the qualities of the optical signal including the bit error rates upon receiving the optical signals using the magnitude of voltage corresponding to the amplitude of the clock measured in the measuring step.